1. Technical Field
This invention is directed to the field of ophthalmic surgery and is specifically directed to methods for the relief of strabismus by the retensioning of ocular muscles using radio frequency modification of collagen in tendons.
2. Background
Strabismus is a misalignment between the two eyes such that the two visual axes do not intersect the point of regard. Between one and four percent of the childhood population is effected by strabismus. "The annual number of surgical operations for strabismus (close to 700,000 or 11 percent of all ophthalmic procedures) is exceeded only by cataract surgery . . . " (National Advisory Eye Council, 1994). Typically, onset is in childhood, but can occur later in life due to lesions in the oculomotor pathway.
Correction of misalignment early in life is central to the development of normal binocular vision and the prevention of amblyopia. Accordingly, strabismus surgery is performed as early in life as possible, and is typically performed under general anesthesia in children and most adults.
In 20% to 50% of patients, repeat surgery is required due to post-operative under- or overcorrection. Repeat surgery places the patient at additional per procedure risk. In addition, secondary surgical procedures are often complicated by the presence of scar tissue and tissue adhesions, with the outcomes being compromised accordingly.
Conventional surgical procedures strengthen the action of an extraocular muscle by resection, advancement, and tucking of the extraocular muscle. In each instance, the muscle's tendon is cut free of the eye at its insertion into the sclera and then sutured back onto the globe. The muscle's tendon may be shortened by cutting off a predetermined amount.
Surgically weakening the action of an extraocular muscle, which is often done in conjunction with strengthening the action of the antagonist, will consist of one of two basic approaches. In one approach the muscle insertion is cut and sutured to the eye at a more posterior position. In the other approach, marginal myotomy, incisions are made part way through the tendon such that the tendon is thinned and elongated.
In the past few years crystallized botulinum toxin, which acts by blocking the release of acetylcholine at the neuromuscular junction, has been used for the temporary partial paralysis of the extraocular muscles. The therapeutic effect with this treatment modality is variable and decreases over time.
Risks associated with conventional strabismus surgery include perforation of the globe when suturing the tendon; variable motor effectiveness, due to the difficulty in quantifying tucking, resection, advancement, and recession procedures; tissue scaring; and tissue adhesions.
Accordingly, there is a need for new surgical techniques and apparatuses that simplify surgical operation and reduce risks associated with strabismus surgery.